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The photosynthetic performance of marine phytoplankton varies in response to a variety of factors, environmental and taxonomic. One of the aims of the MArine primary Production: model Parameters from Space (MAPPS) project of the European Space Agency is to assemble a global database of photosynthesis–irradiance (P-E) parameters from a range of oceanographic regimes as an aid to examining the basin-scale variability in the photophysiological response of marine phytoplankton and to use this information to improve the assignment of P-E parameters in the estimation of global marine primary production using satellite data. The MAPPS P-E database, which consists of over 5000 P-E experiments, provides information on the spatio-temporal variability in the two P-E parameters (the assimilation number, PmB, and the initial slope, αB, where the superscripts B indicate normalisation to concentration of chlorophyll) that are fundamental inputs for models (satellite-based and otherwise) of marine primary production that use chlorophyll as the state variable. Quality-control measures consisted of removing samples with abnormally high parameter values and flags were added to denote whether the spectral quality of the incubator lamp was used to calculate a broad-band value of αB. The MAPPS database provides a photophysiological data set that is unprecedented in number of observations and in spatial coverage. The database will be useful to a variety of research communities, including marine ecologists, biogeochemical modellers, remote-sensing scientists and algal physiologists. The compiled data are available at https://doi.org/10.1594/PANGAEA.874087 (Bouman et al., 2017).

The objective of the current work is to improve our understanding of how water column diatom's abundance and assemblage composition is seasonally transferred from the photic zone to seafloor sediments. To address this, we used a dataset derived from water column, sediment trap and surface sediment samples recovered in the NW Iberian coastal upwelling system. Diatom fluxes (2.2 (±5.6) 106 valves m−2 d−1) represented the majority of the siliceous microorganisms sinking out from the photic zone during all studied years and showed seasonal variability. Contrasting results between water column and sediment trap diatom abundances were found during downwelling periods, as shown by the unexpectedly high diatom export signals when diatom-derived primary production achieved their minimum levels. They were principally related to surface sediment remobilization and intense Minho and Douro river discharge that constitute an additional source of particulate matter to the inner continental shelf. In fact, contributions of allochthonous particles to the sinking material were confirmed by the significant increase of both benthic and freshwater diatoms in the sediment trap assemblage. In contrast, we found that most of the living diatom species blooming during highly productive upwelling periods were dissolved during sinking, and only those resistant to dissolution and the Chaetoceros and Leptocylindrus spp. resting spores were susceptible to being exported and buried. Furthermore, Chaetoceros spp. dominate during spring–early summer, when persistent northerly winds lead to the upwelling of nutrient-rich waters on the shelf, while Leptocylindrus spp. appear associated with late-summer upwelling relaxation, characterized by water column stratification and nutrient depletion. These findings evidence that the contributions of these diatom genera to the sediment's total marine diatom assemblage should allow for the reconstruction of different past upwelling regimes.

Two phytoplankton succession events (September-October 1993 and March 1994) in the Ría de Vigo were studied in relation to their hydrodynamic context. By means of a circulation box model we calculated horizontal and vertical residual fluxes as well as budgets of phytoplankton associated with them. This allowed us to assess the importance of the two factors involved in the selection processes: one hydrodynamic (dependent upon physical dispersion) and one biogeochemical (involving all other processes such as growth, mortality and grazing). The first period was characterised by a downwelling event which produced a reversal of the estuarine circulation pattern (horizontal velocity = 4 km d-1 and downward velocities up to 9 m d-1). This provided suitable conditions for the blooming of Gymnodinium catenatum favoured by its capacity to swim, while the diatom community almost disappeared. The second period corresponded to an upwelling Æ relaxation sequence. During upwelling (horizontal velocity = 6 km d-1; upward velocities up to 12 m d-1), Thalassiosira spp. was dominant. It is suggested that the less energetic conditions associated with the relaxation event (horizontal velocity=1 km d-1; upward velocities < 1 m d-1) favoured the selection of Chatoceros spp. due to its lower sinking rate.

Elemental (C, H, O, N, Si, P) and biochemical composition (proteins, carbohydrates, lipids, phosphorus compounds, chlorophyll and opal) in particulate organic matter, diatoms, other autotrophs, heterotrophs and detritus from natural plankton were established simultaneously by measuring relatively few components. Using standard techniques in marine chemistry on board ship, it is possible to infer a great deal about the composition and condition of the plankton. In addition, the organic matter content in terms of cell volume was determined for each group of plankton. Variation of chemical composition with depth was also considered. The ratio carbohydrates/lipids (Cbh/Lip) was used as an indicator of the chemical quality of the plankton.

A study of the relationship among -O2, ΔN and ΔC was developed when the production or mineralisation of particulate organic matter do not follow the Redfield ratios. A dinoflagellate red tide and a diatom spring bloom are shown as two cases where these Redfield deviations can be found. We propose a new useful tool for modelling water mass mixing and net community production budgets, which includes a chemical parameter ("NCO" = O2 + RN⋅NO3(1-RCS/RC) + RCS⋅CO2) of general application where "NCO" indicates the involved variables (Nitrate-CO2-Oxygen). RN and RC are the fixed Redfield ratios and RCS is the relationship between oxygen consumed and CO2 assimilated corresponding to storage substances. The RCS value depends on the nature of the storage substances. Generally these substances are carbohydrates and the value of RCS=1.

It is frequent to observe disagreements between the relationships RC =-ΔO2/ΔC and RN = -ΔO2/ΔN found during photosynthesis-mineralisation studies in the ocean and those expected according to the Redfield plankton composition. That is because RC and RN depend on the C/N and Carbohydrates/Lipids (Cbh/Lip) ratios of the organic matter. Starting from the mean biochemical composition of the main groups of phytoplankton biomolecules and from the stoichiometry of photosynthesis-mineralisation, we establish a new formulation to enable us to calculate RC and RN as a function of C/N and Cbh/Lip ratios independent of the variance in the N/P ratio. The approach proposed here permits the theoretical limits of RC and RN to be calculated. The RC value can vary between 1 and 1.58 while RN can vary between 5.8 and infinity with the interrelationships between the ratios being defined by RN/RC=C/N which, in its turn, can vary between 3.67 and infinity. For a given RC the limits of RN become narrower and vice versa. When C/N ratio is fixed the limits of the RC and RN values also become narrower. A graphic representation to check and visualise these limits and other experimental biochemical composition values is developed. According to the average value of the Cbh/Lip relationship, 0.82 in carbon, recovered from the literature and for a C/N = 106/16, the estimate mean RC and RN values are 1.41 and 9.33 respectively which are coincident with previous ratios given by other authors.